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- MOV is not a video codec!
- MOV versus MP4
- A Swiss Army knife that ages well
- Strengths of MOV
- Weaknesses of MOV
- Check your MOV files with Treasured
- MOOV, the “brain” of the file
- Structure of QuickTime MOV files
- MOOV is not the “header”
- MDAT is the warehouse
- Making sense of raw data
- How to fix corrupt MOV files
- Why do MOV files become corrupt?
- Reindexing: making inventory
- Solution: Your Repair Kit
MOV is not a video codec!
MOV is the extension used for QuickTime files, a multimedia file format created by Apple in 1991 and used by the production and broadcasting industries.
MOV is not a video or audio codec, but a container format:
- MOV organizes the media — video and audio — inside the file, in several “tracks”
- Each track can be encoded in a different video or audio format
Every book in its place, or it becomes useless.
MOV versus MP4
MP4 container format is directly based on the QuickTime File Format:
- While MP4, being an international standard, has more support through software and hardware vendors, MOV has more features.
- MOV is more oriented towards production, MP4 is more a distribution format and is widely used in consumer video industry.
- MOV and MP4 extensions are interchangeable in most situations
A Swiss Army knife that ages well
Creating the first multimedia container, that remains dominant for over 30 years, is no small feat! Let's examine the strengths and weaknesses of MOV format.
Strengths of MOV
- Workflow-friendly: QuickTime file format has abstract data references and track edit lists, which makes it suited for editing. Thanks to “Reference movies”, MOV can do editing without copying media data, which other container formats can't do.
- Interoperability: MOV can be read and written by a variety of software, including AVID Media Composer, Adobe Premiere, Sony Vegas, GrassValley EDIUS, Da Vinci and Final Cut
- Future-proof: MOV files are codec agnostic, have metadata support, and have unlimited size and duration.
Evidence of MOV vitality: Recent formats Blackmagic RAW and Canon RAW Light are embracing MOV format — albeit hiding the fact under BRAW and CRM extensions.
Weaknesses of MOV
- Fragility: QuickTime file format was not designed for reliance. Missing or bad data at critical locations will make the file unplayable.
- Too many features: QuickTime file format has accumulated over 30 years a lot of byzantine features that are only supported in QuickTime-centric environments. Interoperability with third-party software and devices only happens when the MOV file limits itself to the core features, in other words to the MP4 standard.
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MOOV, the “brain” of the file
Before diving in the details of the MOOV atom, let's examine first how the MOV file is structured, and what is the role of each element.
Structure of QuickTime MOV files
MOV files are structured in atoms that can be nested into many sub-levels, like russian dolls.
QuickTime file format allows for very diverse and complex structures, but the simplest and most common one is populated with 3 top level atoms:
- ftyp — File Type
- mdat — Media Data
- moov — Movie
Top level atoms can be in any order, with the exception of ftyp than must be exactly at the beginning of the file.
ftyp atom contains information about the standards that file conforms to. It is a simple structure with a few dozen bytes only.
mdat atom contains media data, both video and audio, and occupies almost 100% of the file size. During live recording, video and audio data is written in bulk into this section of the QuickTime file.
moov atom is the “brain” of the MOV file. Let's study it in detail.
Let's state it again: MOOV is not the “header”
A common misconception regarding corrupted video repair is that the problem can be solved by adding to the damaged files a small piece of data called a “header”.
This is wrong for MOV files, whose critical element, the moov atom, neither is a small, nor is it located in the “head” of the file.
Indeed, moov atom is a database with dozens of tables, thousands of entries. Not a header by any measure.
QuickTime file format allows for the moov atom to be anywhere inside the file, the most common locations being at the beginning, just after ftyp File Type atom, or at the very end, just after mdat atom containing media data.
In the example on the left, we can see the top level atoms ftyp, wide, mdat, moov and finally udta.
moov structure has nested atoms, up to 6 levels deep.
This MOV file contains 2 tracks (video and audio) and the critical parts are the media tables called stsd, stts, stsc, stsz and stco. Those tables tell the computer where to find each frame inside the file, and how to use it. They are the equivalent to the old card cabinets used in libraries to find books.
If any information in the moov atom is missing or incorrect, the MOV file becomes corrupt and unplayable.
Tools to inspect MOV files
There is a lot of free tools to inspect MOV files: Atomic Parsley, Mp4 Explorer, Dumpster...
This example comes from Atom Inspector, available on Apple Developer website. Note that those tools won't go very far if the MOV file is damaged or one of the atoms is corrupt.
MDAT is the warehouse
Media data is stored in bulk: Video frames and audio blocks are recorded one after another, interleaved and without any header to make identification of those elements easy.
For example, an hypothetical MOV with two text tracks, one in French and one in English, with words counting as frames, would have a mdat atom like this:
LesReprésentantsduPeupleFrançais,WhenintheCourseofhumanevents,constituésenAssembléeNation ale,itbecomesnecessaryforonepeopletodissolvethepoliticalbandswhichhaveconnectedthemwithan other,considérantquel'ignorance,l'oubliouleméprisdesdroitsdel'Hommeandtoassumeamongthepow ersoftheearth,sontlesseulescausesdesmalheurspublicsetdelacorruptiondesGouvernements,ontré solud'exposer,dansuneDéclarationsolennelle,lesdroitsnaturels,inaliénablesetsacrésdel'Homm e,theseparateandequalstationtowhichtheLawsofNatureandofNature'sGodentitlethem,afinquecett eDéclaration,constammentprésenteadecentrespecttotheopinionsofmankindrequiresthattheyshoul ddeclarethecauseswhichimpelthemtotheseparation.àtouslesMembresducorpssocial,leurrappelles anscesseleursdroitsetleursdevoirs;afinquelesactesdupouvoirlégislatif,etceuxdupouvoirexécu tif,pouvantêtreàchaqueinstantcomparésaveclebutdetouteinstitutionpolitique,ensoientplusres pectés;afinquelesréclamationsdescitoyens,fondéesdésormaissurdesprincipessimplesetincontes tables,tournenttoujoursaumaintiendelaConstitutionetaubonheurdetous.
Making sense of raw data
If you know that you should expect French and English words, you can start separating words, and with great effort it becomes readable.
LesReprésentantsduPeupleFrançais,WhenintheCourseofhumanevents,constituésenAssembléeNation
ale,itbecomesnecessaryforonepeopletodissolvethepoliticalbandswhichhaveconnectedthemwithan
other,considérantquel'ignorance,l'oubliouleméprisdesdroitsdel'Hommeandtoassumeamongthepow
ersoftheearth,sontlesseulescausesdesmalheurspublicsetdelacorruptiondesGouvernements,ontré
solud'exposer,dansuneDéclarationsolennelle,lesdroitsnaturels,inaliénablesetsacrésdel'Homm
e,theseparateandequalstationtowhichtheLawsofNatureandofNature'sGodentitlethem,afinquecett
eDéclaration,constammentprésenteadecentrespecttotheopinionsofmankindrequiresthattheyshoul
ddeclarethecauseswhichimpelthemtotheseparation.àtouslesMembresducorpssocial,leurrappelles
anscesseleursdroitsetleursdevoirs;afinquelesactesdupouvoirlégislatif,etceuxdupouvoirexécu
tif,pouvantêtreàchaqueinstantcomparésaveclebutdetouteinstitutionpolitique,ensoientplusres
pectés;afinquelesréclamationsdescitoyens,fondéesdésormaissurdesprincipessimplesetincontes
tables,tournenttoujoursaumaintiendelaConstitutionetaubonheurdetous.
Les Représentants du Peuple Français, When in the Course of human events, constitués en Assemblée Nationale, it becomes necessary for one people to dissolve the political bands which have connected them with another, considérant que l'ignorance, l'oubli ou le mépris des droits de l'Homme and to assume among the powers of the earth, sont les seules causes des malheurs publics et de la corruption des Gouvernements, ont résolu d'exposer, dans une Déclaration solennelle, les droits naturels, inaliénables et sacrés de l'Homme, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, afin que cette Déclaration, constamment présente a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation. à tous les Membres du corps social, leur rappelle sans cesse leurs droits et leurs devoirs ; afin que les actes du pouvoir législatif, et ceux du pouvoir exécutif, pouvant être à chaque instant comparés avec le but de toute institution politique, en soient plus respectés ; afin que les réclamations des citoyens, fondées désormais sur des principes simples et incontestables, tournent toujours au maintien de la Constitution et au bonheur de tous.
Even armed with French and English dictionaries, separating the words is quite challenging.
In some cases several solutions are possible: take humanevents for example.
You could split it into human events or a more picturesque humane vents, both make sense in English.
Therefore reading (in computer jargon we say parsing) media data is very hard, it requires heuristic methods and will not always to give the intended result.
This is why the moov section, in addition to track descriptions, includes an index that tells where each frame (word) starts and ends.
moov index consists in several tables with address, size, time, duration, and display order information for each frame of each track. Using this information, the media data starts to make sense:
considérant que l'ignorance, l'oubli ou le mépris des droits de l'Homme
sont les seules causes des malheurs publics et de la corruption des
Gouvernements, ont résolu d'exposer, dans une Déclaration solennelle,
les droits naturels, inaliénables et sacrés de l'Homme, afin que cette
Déclaration, constamment présente à tous les Membres du corps social,
leur rappelle sans cesse leurs droits et leurs devoirs ; afin que les
actes du pouvoir législatif, et ceux du pouvoir exécutif, pouvant être
à chaque instant comparés avec le but de toute institution politique,en
soient plus respectés ; afin que les réclamations des citoyens, fondées
désormais sur des principes simples et incontestables, tournent toujours
au maintien de la Constitution et au bonheur de tous.
it becomes necessary for one people
to dissolve the political bands
which have connected them with
another, and to assume among the
powers of the earth, the separate
and equal station to which the Laws
of Nature and of Nature's God
entitle them, a decent respect to
the opinions of mankind requires
that they should declare the causes
which impel them to the separation.
Without a moov atom to make sense of it, the mdat section of a video file is a “soup” of raw data.
Now let's see how to repair a corrupted MOV file, by interpreting the raw data and re-building the moov atom...
How to fix corrupt MOV files
Why do MOV files become corrupt?
All the cases we have seen over the years fall into one of those categories:
- If audio/video recording ends abruptly, the MOV file will lack the moov atom that gives sense to video and audio data stored in bulk in the file. Reindexing will be needed. (see below)
- If the MOV file has been undeleted or recovered from a formatted card, its moov and its mdat probably don't match. It will need reindexing as well.
- If the MOV contains a moov atom but doesn't play, there are inconsistencies in the database. If we are lucky, this can be fixed by container structure correction.
Reindexing: making an inventory of the warehouse
To make the corrupt MOV file playable, the moov database has to be recreated.
Media data stored in bulk inside the file has to be parsed. As seen in the “French and English words” example above, this is not a deterministic task.
A heuristic algorithm specific to the type of media — French words, English words — has to be developed. It has to be very specific and use probabilities to determine if a piece of data is more likely to be video or audio, and where it exactly starts and ends.
The animation below shows the different operations of a repair through reindexing:
Filtering, Parsing, Indexing and Wrapping.
One minute of video contains around 4000 frames of audio and video. For every minute of corrupted footage it processes, a repair tool has to correctly identify those 4000 elements stored in bulk inside the file. Taking into account that encoded video and audio don't contain patterns that can easily be identified — that would go against compression performance — the task is complex.
A repair tool that misidentifies only 1 out of 1000 elements will cause an average of four glitches per minute of video repaired. That would be unacceptable.
This is why Aero Quartet develops unique tools for every request it receives. Our tools are configured to identify exactly one type of video and one type of audio, and this gives them a level of quality that generic repair tools can't achieve.
Solution: Your Repair Kit, developed by our technicians
Our team of technicians will prepare the specific Repair Kit that can fix your files and guarantee a perfect result.
To get started, try Treasured on your files, or click on Live Assistance to chat with the team.
